Re: [PATCH 00/27] ext4: use iomap for regular file's buffered I/O path and enable large folio

Sedat Dilek
2024-10-22T07:00:26Z

On Tue, Oct 22, 2024 at 5:13 AM Zhang Yi <yi.zhang@huaweicloud.com> wrote:
>
> From: Zhang Yi <yi.zhang@huawei.com>
>
> Hello！
>
> This patch series is the latest version based on my previous RFC
> series[1], which converts the buffered I/O path of ext4 regular files to
> iomap and enables large folios. After several months of work, almost all
> preparatory changes have been upstreamed, thanks a lot for the review
> and comments from Jan, Dave, Christoph, Darrick and Ritesh. Now it is
> time for the main implementation of this conversion.
>
> This series is the main part of iomap buffered iomap conversion, it's
> based on 6.12-rc4, and the code context is also depend on my anohter
> cleanup series[1] (I've put that in this seris so we can merge it
> directly), fixed all minor bugs found in my previous RFC v4 series.
> Additionally, I've update change logs in each patch and also includes
> some code modifications as Dave's suggestions. This series implements
> the core iomap APIs on ext4 and introduces a mount option called
> "buffered_iomap" to enable the iomap buffered I/O path. We have already
> supported the default features, default mount options and bigalloc
> feature. However, we do not yet support online defragmentation, inline
> data, fs_verify, fs_crypt, ext3, and data=journal mode, ext4 will fall
> to buffered_head I/O path automatically if you use those features and
> options. Some of these features should be supported gradually in the
> near future.
>
> Most of the implementations resemble the original buffered_head path;
> however, there are four key differences.
>
> 1. The first aspect is the block allocation in the writeback path. The
> iomap frame will invoke ->map_blocks() at least once for each dirty
> folio. To ensure optimal writeback performance, we aim to allocate a
> range of delalloc blocks that is as long as possible within the
> writeback length for each invocation. In certain situations, we may
> allocate a range of blocks that exceeds the amount we will actually
> write back. Therefore,
> 1) we cannot allocate a written extent for those blocks because it may
> expose stale data in such short write cases. Instead, we should
> allocate an unwritten extent, which means we must always enable the
> dioread_nolock option. This change could also bring many other
> benefits.
> 2) We should postpone updating the 'i_disksize' until the end of the I/O
> process, based on the actual written length. This approach can also
> prevent the exposure of zero data, which may occur if there is a
> power failure during an append write.
> 3) We do not need to pre-split extents during write-back, we can
> postpone this task until the end I/O process while converting
> unwritten extents.
>
> 2. The second reason is that since we always allocate unwritten space
> for new blocks, there is no risk of exposing stale data. As a result,
> we do not need to order the data, which allows us to disable the
> data=ordered mode. Consequently, we also do not require the reserved
> handle when converting the unwritten extent in the final I/O worker,
> we can directly start with the normal handle.
>
> Series details:
>
> Patch 1-10 is just another series of mine that refactors the fallocate
> functions[1]. This series relies on the code context of that but has no
> logical dependencies. I put this here just for easy access and merge.
>
> Patch 11-21 implement the iomap buffered read/write path, dirty folio
> write back path and mmap path for ext4 regular file.
>
> Patch 22-23 disable the unsupported online-defragmentation function and
> disable the changing of the inode journal flag to data=journal mode.
> Please look at the following patch for details.
>
> Patch 24-27 introduce "buffered_iomap" mount option (is not enabled by
> default now) to partially enable the iomap buffered I/O path and also
> enable large folio.
>
>
> About performance:
>
> Fio tests with psync on my machine with Intel Xeon Gold 6240 CPU with
> 400GB system ram, 200GB ramdisk and 4TB nvme ssd disk.
>
> fio -directory=/mnt -direct=0 -iodepth=$iodepth -fsync=$sync -rw=$rw \
> -numjobs=${numjobs} -bs=${bs} -ioengine=psync -size=$size \
> -runtime=60 -norandommap=0 -fallocate=none -overwrite=$overwrite \
> -group_reportin -name=$name --output=/tmp/test_log
>

Hi Zhang Yi,

can you clarify about the FIO values for the diverse parameters?

Thanks.

BR,
-Sedat-

> == buffer read ==
>
> buffer_head iomap + large folio
> type bs IOPS BW(MiB/s) IOPS BW(MiB/s)
> -------------------------------------------------------
> hole 4K 576k 2253 762k 2975 +32%
> hole 64K 48.7k 3043 77.8k 4860 +60%
> hole 1M 2960 2960 4942 4942 +67%
> ramdisk 4K 443k 1732 530k 2069 +19%
> ramdisk 64K 34.5k 2156 45.6k 2850 +32%
> ramdisk 1M 2093 2093 2841 2841 +36%
> nvme 4K 339k 1323 364k 1425 +8%
> nvme 64K 23.6k 1471 25.2k 1574 +7%
> nvme 1M 2012 2012 2153 2153 +7%
>
>
> == buffer write ==
>
> buffer_head iomap + large folio
> type Overwrite Sync Writeback bs IOPS BW IOPS BW(MiB/s)
> ----------------------------------------------------------------------
> cache N N N 4K 417k 1631 440k 1719 +5%
> cache N N N 64K 33.4k 2088 81.5k 5092 +144%
> cache N N N 1M 2143 2143 5716 5716 +167%
> cache Y N N 4K 449k 1755 469k 1834 +5%
> cache Y N N 64K 36.6k 2290 82.3k 5142 +125%
> cache Y N N 1M 2352 2352 5577 5577 +137%
> ramdisk N N Y 4K 365k 1424 354k 1384 -3%
> ramdisk N N Y 64K 31.2k 1950 74.2k 4640 +138%
> ramdisk N N Y 1M 1968 1968 5201 5201 +164%
> ramdisk N Y N 4K 9984 39 12.9k 51 +29%
> ramdisk N Y N 64K 5936 371 8960 560 +51%
> ramdisk N Y N 1M 1050 1050 1835 1835 +75%
> ramdisk Y N Y 4K 411k 1609 443k 1731 +8%
> ramdisk Y N Y 64K 34.1k 2134 77.5k 4844 +127%
> ramdisk Y N Y 1M 2248 2248 5372 5372 +139%
> ramdisk Y Y N 4K 182k 711 186k 730 +3%
> ramdisk Y Y N 64K 18.7k 1170 34.7k 2171 +86%
> ramdisk Y Y N 1M 1229 1229 2269 2269 +85%
> nvme N N Y 4K 373k 1458 387k 1512 +4%
> nvme N N Y 64K 29.2k 1827 70.9k 4431 +143%
> nvme N N Y 1M 1835 1835 4919 4919 +168%
> nvme N Y N 4K 11.7k 46 11.7k 46 0%
> nvme N Y N 64K 6453 403 8661 541 +34%
> nvme N Y N 1M 649 649 1351 1351 +108%
> nvme Y N Y 4K 372k 1456 433k 1693 +16%
> nvme Y N Y 64K 33.0k 2064 74.7k 4669 +126%
> nvme Y N Y 1M 2131 2131 5273 5273 +147%
> nvme Y Y N 4K 56.7k 222 56.4k 220 -1%
> nvme Y Y N 64K 13.4k 840 19.4k 1214 +45%
> nvme Y Y N 1M 714 714 1504 1504 +111%
>
> Thanks,
> Yi.
>
> Major changes since RFC v4:
> - Disable unsupported online defragmentation, do not fall back to
> buffer_head path.
> - Wite and wait data back while doing partial block truncate down to
> fix a stale data problem.
> - Disable the online changing of the inode journal flag to data=journal
> mode.
> - Since iomap can zero out dirty pages with unwritten extent, do not
> write data before zeroing out in ext4_zero_range(), and also do not
> zero partial blocks under a started journal handle.
>
> [1] https://lore.kernel.org/linux-ext4/20241010133333.146793-1-yi.zhang@huawei.com/
>
> ---
> RFC v4: https://lore.kernel.org/linux-ext4/20240410142948.2817554-1-yi.zhang@huaweicloud.com/
> RFC v3: https://lore.kernel.org/linux-ext4/20240127015825.1608160-1-yi.zhang@huaweicloud.com/
> RFC v2: https://lore.kernel.org/linux-ext4/20240102123918.799062-1-yi.zhang@huaweicloud.com/
> RFC v1: https://lore.kernel.org/linux-ext4/20231123125121.4064694-1-yi.zhang@huaweicloud.com/
>
>
> Zhang Yi (27):
> ext4: remove writable userspace mappings before truncating page cache
> ext4: don't explicit update times in ext4_fallocate()
> ext4: don't write back data before punch hole in nojournal mode
> ext4: refactor ext4_punch_hole()
> ext4: refactor ext4_zero_range()
> ext4: refactor ext4_collapse_range()
> ext4: refactor ext4_insert_range()
> ext4: factor out ext4_do_fallocate()
> ext4: move out inode_lock into ext4_fallocate()
> ext4: move out common parts into ext4_fallocate()
> ext4: use reserved metadata blocks when splitting extent on endio
> ext4: introduce seq counter for the extent status entry
> ext4: add a new iomap aops for regular file's buffered IO path
> ext4: implement buffered read iomap path
> ext4: implement buffered write iomap path
> ext4: don't order data for inode with EXT4_STATE_BUFFERED_IOMAP
> ext4: implement writeback iomap path
> ext4: implement mmap iomap path
> ext4: do not always order data when partial zeroing out a block
> ext4: do not start handle if unnecessary while partial zeroing out a
> block
> ext4: implement zero_range iomap path
> ext4: disable online defrag when inode using iomap buffered I/O path
> ext4: disable inode journal mode when using iomap buffered I/O path
> ext4: partially enable iomap for the buffered I/O path of regular
> files
> ext4: enable large folio for regular file with iomap buffered I/O path
> ext4: change mount options code style
> ext4: introduce a mount option for iomap buffered I/O path
>
> fs/ext4/ext4.h | 17 +-
> fs/ext4/ext4_jbd2.c | 3 +-
> fs/ext4/ext4_jbd2.h | 8 +
> fs/ext4/extents.c | 568 +++++++++++----------------
> fs/ext4/extents_status.c | 13 +-
> fs/ext4/file.c | 19 +-
> fs/ext4/ialloc.c | 5 +
> fs/ext4/inode.c | 755 ++++++++++++++++++++++++++++++------
> fs/ext4/move_extent.c | 7 +
> fs/ext4/page-io.c | 105 +++++
> fs/ext4/super.c | 185 ++++-----
> include/trace/events/ext4.h | 57 +--
> 12 files changed, 1153 insertions(+), 589 deletions(-)
>
> --
> 2.46.1
>
>